The invention pertains to a process for treating subterranean zones, particularly oil and gas wells where incompetent or weak formations are encountered, with lightweight, aqueous hydraulic cement slurry and a composition useful in this process. In cementing particularly long strings of pipe in a wellbore, i.e., one or two thousand feet or more, it is often necessary to perform the cement job in multiple stages because the excessive weight of the long column of cement slurry would fracture the subterranean formation.
Cement slurries comprising hydraulic cements, bentonite and large amounts of water have been employed in well cementing where a lightweight slurry is desired. Sodium metasilicate has also been employed in cement slurries in well cementing. Cellulose derivates have likewise been employed in well cement slurries in the past.
In order to cement long strings of pipe, oil and gas producers have previously resorted to multiple-stage cement jobs with resultant extended lost rig time or have used more expensive additives such as glass or ceramic microbubbles to lighten cementing slurries. Previous water-extended lightweight slurries employing bentonite or sodium metasilicate have generally suffered from poor performance due to excessive free water content or lack of reasonable setting time or ultimate strength.